Foundation systems typically employ piles driven into bedrock or below, in order to provide support for a foundation. Often, it is necessary to drive piles of a defined length into the ground and to bedrock employing cranes and pile-driving equipment. Where there is a limitation on the employment of pile-driving equipment or cranes, such as a limitation on height, and where prior pile-driving is not practical, a system known as the minipile system has been employed comprising a plurality of solid metal bar pilings coupled together through threaded connections at the end of each bar. Such a system is particularly adapted for use in putting support pilings into existing foundations and facilities.
Generally, the system comprises providing a load-bearing coupled pile system for foundations, by drilling a substantially vertical hole in the ground, employing an outer casing drill, such as, for example, 8 to 10 inches, and an inner counter-rotating pile drill of 4 to 6 inches, and drilling a hole through to bedrock or, for example, up to 20 feet into the bedrock. A hollow casing is then inserted into the drilled hole, and later solid metal pile rods of a length, depending on the space available, and typically ranging from 4 to 15 feet, are coupled together at their ends, to connect together the round, solid-steel pile rods or bars. The coupled bars or rods are then lowered into the pipe casing and inserted or driven into the ground, in order to provide a supported load-bearing function for the foundation.
The piles are coupled together merely to hold the sections of the bars together, while they are lowered into the pipe casing. Typically, spacers, such as plastic spacers, are employed at defined lengths, for example 10 feet, within the pipe casings, to provide for generaly vertical alignment of the coupled rods or bars within the pipe casings. For example, strength is a significant factor in such a system, since a solid bar; for example 61/4 inches in diameter, weighs approximately 105 pounds per linear feet and at, for example, a 160-foot depth, approximately 81/2 tons are to be carried by the upper couplings, so that all pile couplings are designed to carry the total weight of the foundation, regardless if it is an upper or a lower coupled pile. After the coupled bars are lowered into the pipe casing and the lower end of the bar is resting on bedrock or below, the pipe casing around the bar is filled or injected with a liquid concrete between the outside diameter of the bar and the inside diameter of the pipe casing, thereby providing a foundation system. On hardening of the concrete within the pipe casing, the couplings employed in securing the bars together no longer have any affect on the installation of the bars.
In one present system, threaded couplings are employed at each end of the solid-steel bars being used, which threaded couplings require time-consuming and costly machining of the bars at each end, plus manufacturing the threaded coupling, in order to provide for a threaded connection between the bars. The present coupling system being used also requires a starting thread at the end of each bar and screwing the coupling onto each end of the bars, to join together the coupled bars. If the bars are not aligned almost perfectly, then the threads will not engage and may become cross-threaded. In addition and importantly, such a threaded system requires a careful control of the tension, since the weight of the bar or rod must be maintained such that not too much weight is placed on the upper end of the bar being threaded, since, if too much weight is applied, there is danger of deforming the threads on the bar.
Furthermore, in the threaded pile-coupling system, each of the bars is required, typically by code or by architectural design, to have 99% or over contact between the ends of the bars, so as to prevent any even slight movement of the bars, once a load-bearing structure is applied. The system of turning a threaded coupling onto the end of a threaded bar and then screwing another threaded bar into this coupling presents a practical problem, in that it is difficult to ascertain and prove that the two threaded bars at the end are in full support and load-bearing contact with each other across the entire end area. Presently, in order to insure such contact, a hole is machined into the threaded coupling at midpoint, which hole is employed as an inspection hole, to permit visual inspection of each bar, to ascertain that there is full end bar-to-bar contact after the threading operation. Thus, the threaded-coupling system, while avoiding some of the difficulties associated with pile-driving, requires expensive machining of the couplings expensive machining of the bars, possible damage to the threads due to handing during the threading operation, the slow assembly of the coupling to the bar and the need to make visual inspection, to ascertain bar-to-bar contact.
Therefore, it is desirable to provide an improved coupling for sectional bars or piles used in foundation systems, in order to overcome the disadvantages of the present threaded-coupling system.